1. Field of the Invention
The present invention relates to an ink jet head. The ink jet head is utilized in a device that prints words, images, etc. by discharging ink toward a print medium. The ink jet head is utilized in, for example, an ink jet printer, a copier, a fax machine, a multifunctional product, etc.
2. Description of the Related Art
A normal ink jet head comprises a passage unit and an actuator unit. The passage unit comprises a nozzle and a pressure chamber. The nozzle discharges ink toward a print medium. The pressure chamber is filled with ink. The pressure chamber communicates with the nozzle.
The actuator unit may be stacked on the passage unit. The actuator unit may be a type having a piezoelectric element. The piezoelectric element may include a piezoelectric layer, a first electrode connected with a front surface of the piezoelectric layer, a second electrode connected with a back surface of the piezoelectric layer, and an intermediate layer located between the second electrode and the passage unit. The piezoelectric layer contracts in a planar direction when a potential difference is applied between the first electrode and the second electrode. The first electrode, the second electrode, and the intermediate layer are unable to contract in the planar direction. As a result, the force for causing the piezoelectric layer to contract in the planar direction is transformed into a force for deforming the entire piezoelectric element in a direction of thickness. The piezoelectric element is deformed toward the pressure chamber by applying potential difference between the first electrode and the second electrode. When the piezoelectric element deforms towards the pressure chamber, the volume of the pressure chamber decreases. The pressure of the ink within the pressure chamber is increased, and the ink is discharged from the nozzle. When the potential difference between the first electrode and the second electrode is cancelled, the state in which the piezoelectric element is deformed towards the pressure chamber is released. The volume of the pressure chamber consequently increases, and ink is drawn into the pressure chamber from an ink chamber.
When the intermediate layer is present between the second electrode and the passage unit, the entire piezoelectric element deforms by a greater amount in the direction of thickness. An insulating layer is usually utilized in this intermediate layer. By using this configuration, the pressure within the pressure chamber can be increased and decreased efficiently. An ink jet head having the above configuration is taught in, for example, U.S. Pat. No. 6,672,715.
When, for example, a print medium (printing paper for example) is charged, an electric charge may move from the print medium to the passage unit. The passage unit is thus charged, and the potential of the passage unit may become greater than the potential of the second electrode. In this case, components of the ink (such as hydrogen ions) within the passage unit may be attracted toward the actuator unit (the second electrode), and may penetrate into the actuator unit. When, for example, hydrogen ions have penetrated the actuator unit, hydrogen gas may be formed within the actuator. When hydrogen gas is formed within the actuator unit, the layers within the actuator unit (for example the piezoelectric layer and the second electrode) may peel off.
In the conventional technique (U.S. Pat. No. 6,672,715), the second electrode is exposed at a side surface of the actuator unit. A conductive adhesive is applied across a front surface of the passage unit from the exposed part of the second electrode. The second electrode and the passage unit are thus electrically connected, and the second electrode and the passage unit therefore maintain an approximately identical potential. The components of the ink within the passage unit can thus be prevented from penetrating into the actuator unit.